Fastening of sheet material

Abstract

A fastener such as a self piercing rivet ( 1 ) is inserted into sheet material ( 19 ) without full penetration such that the deformed end of the rivet remains encapsulated by an upset annulus of the sheet material ( 19 ). The sheet material ( 19 ) is clamped between a nose ( 17 ) and a die ( 16 ) of a riveting machine. Once the sheet material ( 19 ) is clamped, the distance between the nose ( 17 ) and the die ( 16 ) is controlled during the riveting operation by a restraint device ( 20, 23 ). This technique ensures that reaction forces generated in the joint between the nose ( 17 ) and the die ( 16 ) during riveting are absorbed in the joint as compressive stresses during the riveting operation so that the resulting joint has improved fatigue life. Furthermore, the rivet insertion load imparted into the C frame as a reaction force is applied back into the joint as a post rivet-insertion clamping load. Alternatively, a separate clamping force is applied after the rivet ( 1 ) has been inserted.

What is claimed is:  
     
       1. A method for inserting a fastener ( 1 ) into sheet material ( 5 ,  6 ) comprising inserting the fastener ( 1 ) into at least one sheet without full penetration such that a deformed end of the fastener remains encapsulated by an upset annulus of the sheet material, the sheet material ( 5 ,  6 ) being disposed between a nose ( 17 ) and a die ( 16 ) of fastening apparatus ( 18 ) and the fastener ( 1 ) being inserted into the sheet material by means of a punch that is reciprocal relative to the nose ( 17 ), characterized in that a first clamping force is applied to the sheet material during fastener insertion between the nose and die in the region around the fastener insertion location, and in that after the fastener is inserted the punch is retracted and then a second clamping force is applied to the sheet material ( 2 ,  3 ) between the nose ( 17 ) and die ( 16 ) in the region around the fastener insertion location so as to reduce deformation of the sheet out of its plane in the region around the fastener insertion location. 
     
     
       2. A method for inserting a fastener according to  claim 1 , the nose ( 17 ) being supported by a support member ( 20 ), characterized in that movement of the nose ( 17 ) relative to the support member ( 20 ) in a direction away from the die is prevented during the fastening operation. 
     
     
       3. A method for inserting a fastener according to to  claim 1 , wherein a clamping force is also applied to the sheet material ( 5 ,  6 ) prior to the fastener being inserted. 
     
     
       4. A method for inserting a fastener according to  claim 1 , wherein the second clamping force and the force required to insert the fastener ( 1 ) are derived from the same actuator. 
     
     
       5. A method for inserting a fastener according to  claim 1 , wherein the second clamping force applied after insertion of the fastener ( 1 ) is varied by varying the force applied to insert the fastener ( 1 ). 
     
     
       6. A method for inserting a fastener according to  claim 1 , wherein the punch is retracted whilst the sheet material is under load by the first clamping force. 
     
     
       7. A panel clinching method wherein two or more sheets of material ( 5 ,  6 ) are deformed into locking engagement, the sheet material being disposed between a nose ( 17 ) and a die ( 16 ) of fastening apparatus, the sheet material ( 5 ,  6 ) being deformed by means of a punch that is reciprocal relative to the nose ( 17 ), characterized in that a first claming force is applied to the sheet material during fastener insertion between the nose and die in the region around the fastener insertion location, and in that after the sheets are deformed by the punch, the punch is retracted and then a second clamping force is applied to the sheet material between the nose ( 17 ) and die ( 16 ) in the region around the punch insertion location so as to reduce deformation of the sheet ( 5 ,  6 ) out of its plane in the region around the punch insertion location.